At present, owing to its advantages such as low power consumption, small size, long service life, avoidance of mercury and no environmental pollution etc., the light emitting diode (LED) is widely used in the field of special lighting, such as automobiles, back light, traffic lights, industrial equipment, instrumentation panels. With improvements of the performance of LED, LED is expected to replace traditional light sources such as fluorescent light, incandescent light and becomes the fourth-generation light source.
Early LED enclosure materials are mostly epoxy resin which has the advantages like higher refractive index and good adhesion properties etc., but also obvious drawbacks in terms of weatherability and yellowing resistance. Silicone rubber, however, possesses a series of excellent performances such as excellent weatherability, heat resistance and yellowing resistance, and thus the application of silicone rubber in the LED enclosure has represented the development trend nowadays. For use of silicone rubber material as LED enclosure materials, there are still some outstanding technical problems to be resolved, such as adhesion force with PPA (polyphthalamide resin) and metal, good light transmittance and storage stability of the product, and so on. Normally, the adhesion property may be improved by simply adding various silane coupling agents. But in most cases it is difficult to balance the requirements on adhesion and transmittance, or there occurs turbidity during the storage of the product resulting in various problems such as less transparency and shorter shelf life accordingly.
In order to achieve both good adhesion to various enclosure materials made of thermoplastic material, for example PPA, or to the electrodes made of metals, for example Ag and Au, and also take the excellent transparency into consideration, it is proposed in prior art that the specific organic polysiloxane component having the refractive index difference falling within a very narrow range (such as below 0.03) is used as the matrix of the silicone rubber composition, with generally adding metallic condensation catalyst such as aluminum metal chelate catalyst to facilitate the coupling and adhesion. However, such a technical solution limits the material selection for the silicone rubber composition. Moreover, although it is shown from mechanism and some experimental data that the metallic condensation catalyst such as aluminum metal chelate catalyst can facilitate the adhesion to some extent, the catalyst extremely trends to react with e.g. air under normal operating conditions in practical application, resulting in catalyst deterioration and adverse effect on use. In industrial production, some special control processes are required in order to avoid this problem.
In addition, CN101935455A proposes an organic silicone material for LED enclosure and the method for preparing the same, which improve optical property, mechanical property and adhesion force to the bracket at the same time. Vinyl polysiloxane, hydrogen-containing polysiloxane and vinyl MQ resin are used as main components of the inventive composition, wherein the mixture of various coupling agents and catalysts such as trimethoxysilane, n-butyl titanate are also used. However, if there are no restrictions on selecting coupling agents and only the adhesive force is considered, many selected coupling agents may render the product turbid or slightly white due to slow hydrolysis during storage, thereby affecting the transmittance and storage period of the final product.